ANS-C01 Network Design Practice Question
A company wants to ensure that traffic between EC2 instances in the same VPC but different subnets is encrypted. Which solution should be used?
⚠ Common exam trap
It's easy for candidates to confuse network-layer access control (security groups, NACLs) with encryption, assuming that allowing traffic through a firewall or using VPC Peering inherently secures the data, when in fact neither provides confidentiality or integrity of the payload.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use IPsec VPN between the instances.
An IPsec VPN between EC2 instances creates an encrypted tunnel at Layer 3, ensuring that all traffic between the instances is encrypted regardless of the underlying network path. This is necessary because traffic within a VPC traversing different subnets is not encrypted by default, even though it stays within the AWS network.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use security groups to allow traffic.
Why it's wrong here
Security groups are firewalls, not encryption.
- ✗
Use VPC Peering.
Why it's wrong here
VPC Peering does not encrypt traffic.
- ✗
Use network ACLs to allow traffic.
Why it's wrong here
NACLs are stateless firewalls, not encryption.
- ✓
Use IPsec VPN between the instances.
Why this is correct
IPsec provides encryption for traffic between instances.
Visual reference
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.